In an internal combustion engine, some of air-fuel mixture introduced into a combustion chamber leaks into the crankcase through the gap between the piston and the cylinder. The leaked air-fuel mixture, which is referred to as blow-by gas, causes degradation of oil. Therefore, in an internal combustion engine installed in a vehicle, ventilation of the blow-by gas is performed using the negative pressure of intake air to draw the blow-by gas inside the crankcase. The blow-by gas drawn from the crankcase is incorporated in the intake air and the blow-by gas is treated by being combusted together with new air-fuel mixture inside the combustion chamber.
In an internal combustion engine provided with a forced-induction device, such as a turbocharger, the ventilation of the blow-by gas using the drawing-in by the intake negative pressure cannot be performed during forced induction, at which the intake air pressure is positive. Therefore, conventionally, a blow-by gas ventilation device, such as that described in Patent Document 1, has been proposed. The blow-by gas ventilation device described in this document includes a bypass passage, which connects portions of an intake passage at an upstream side and a downstream side of a forced-induction device, and an ejector installed in the bypass passage. The ejector is a device that draws an intake gas using a negative static pressure formed about a jet flow of drive gas of which the flow velocity is increased. With this conventional blow-by gas ventilation device, the ejector is installed so that the intake air flowing through the bypass passage operates as the drive gas to draw the blow-by gas inside the crankcase.
In the blow-by gas ventilation device, which includes such an ejector, during forced induction operation of the internal combustion engine, the intake air flows through the bypass passage due to the internal differential pressure between intake passage portions upstream and downstream of the forced-induction device. In this process, the ejector operates using the intake air flowing through the bypass passage as the drive gas to draw the blow-by gas from the crankcase. The blow-by gas drawn from the crankcase is introduced, together with the intake air flowing through the bypass passage, into the portion of the intake passage at the upstream side of the forced-induction device.